Method for machining a high pressure fuel accumulator, high pressure fuel accumulator and connector branches for using said method

ABSTRACT

The invention relates to a method for machining a common rail for a common rail fuel injection system of an internal combustion engine, having a base body, which is equipped with a plurality of connection openings. The invention also relates to a common rail and to a connection stub for application of the method. In the method, the base body is deformed in the region of the connection openings. In the region of each of the connection openings, one through bore is provided, which has two segments of different-sized internal diameters. The connection stub of the invention is characterized in that the outside diameter of the connection stub, on its end toward the common rail, is substantially equivalent to the internal diameter of the segment of the through bore in the common rail having the larger diameter.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 00/03246 filed onSep. 19, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for machining a common rail for acommon rail fuel injection system of an internal combustion engine,having a base body, which is equipped with a plurality of connectionopenings. The invention also relates to a common rail and to aconnection stub for application of the method.

2. Description of the Prior Art

In common rail fuel injection systems, a high-pressure pump, optionallywith the aid of a prefeed pump, pumps the fuel to be injected out of atank into the central high-pressure fuel reservoir, which is also calleda common rail. From the rail, fuel lines lead to the various injectorsthat are assigned one to each of the cylinders of the engine. To injectfuel into the combustion chamber of the engine, the injectors aretriggered individually by the engine electronics as a function of theengine operating parameters. By means of the common rail, the pressuregeneration and the injection are decoupled from one another. Oneconventional common rail is described for instance in German PatentDisclosure DE 195 48 611. The conventional common rail withstandspressures of up to about 1100 bar.

OBJECTS AND SUMMARY OF THE INVENTION

The primary object of the invention is to increase the high-pressurestrength of the known common rail by simple provisions.

In a method for machining a common rail for a common rail fuel injectionsystem of an internal combustion engine, having a base body, which isequipped with a plurality of connection openings, this object isattained in that the base body is deformed in the region of theconnection openings. Within the context of the present invention, it hasbeen demonstrated that the high-pressure strength of the common rail islimited primarily by the intersections between the connection openingsand the base body. In the region of the transitions between theconnection openings and the base body, high tensile forces occur duringoperation. By rounding them off, the transitions between the connectionopenings and the base body can be made no longer sharp. As a result, thehigh-pressure strength of the common rail can be enhanced. However, therounding entails very great effort and high cost. By the mechanicaldeformation, according to the invention, of the base body, thehigh-pressure strength of the common rail is enhanced in a much simplerway. The common rail of the invention withstands pressures of over 2000bar. Advantageously, the provisions according to the invention can becombined with the known provisions, such as rounding the intersections,in order to achieve even better results. The teaching of the inventioncan also be combined with an eccentric disposition of the connectionopenings.

A particular embodiment of the method of the invention is characterizedin that the base body, in the region of the connection openings, iselastically deformed from outside with the aid of a connection stub. Bythe mechanical deformation of the base body in the critical region ofthe intersections, intrinsic pressure stresses are introduced into theregion of the intersections. By means of the internal pressureprevailing in the interior of the base body during operation of thecommon rail, the intrinsic pressure stresses generated in thepressureless state are cancelled out. As a result, the region of thebase body that has critical tensile stresses is markedly reduced insize.

In a common rail for application of the method described above, theabove-stated object is attained in that in the region of each of theconnection openings, one through bore is provided, which has twosegments of different-sized internal diameters. By means of the elasticdeformation from outside, the bottom of the connection opening, formedby the segment of the through bore having the smaller internal diameter,is deformed inward elastically.

A particular feature of the common rail of the invention ischaracterized in that a female thread is embodied in the segment of thethrough bore having the larger internal diameter. The female threadserves to receive a connection stub, which in turn serves to connecthigh-pressure fuel lines.

In a connection stub for application of the above-described method, theabove-stated object is attained in that the outside diameter of theconnection stub, on its end toward the common rail, is substantiallyequal to the internal diameter of the larger diameter segment of thethrough bore in the common rail. Upon assembly of the connection stub ofthe invention, the end of the connection stub toward the common rail ispressed against the bottom of the connection opening. As a result, onthe one hand the connection opening is sealed off from its surroundings,and on the other, the desired deformation of the bottom of theconnection opening is attained.

A particular feature of the connection stub of the invention ischaracterized in that on the end of the connection stub toward thecommon rail, a male thread is embodied that is complimentary to thefemale thread of the through bore. Via the thread, the contact pressurerequired for the sealing and the deformation is generated. By means of adefined tightening moment and a suitable geometry of the region to bedeformed, the magnitude and the direction of the deformation of thecritical region of the connection opening can be adjusted.

A further feature of the method of the invention is that in the basebody, a rigid internal tube is disposed whose outer contour correspondsto the desired inner contour of the base body in the region of theconnection openings, and in that the base body, in the region of theconnection openings, is deformed from outside plastically inward with atool. According to the present invention, the base body is compressedinward in the region of the transitions between the connection openingsand the base body. The internal tube serves in a sense as a template forthe base body in the region of the connection openings and remains inthe base body after the deformation. By the deformation of the basebody, the region of the greatest tensile stress is removed from theregion of the intersection, which has an advantageous effect on thehigh-pressure strength of the common rail.

A further feature of the method of the invention is that the internaltube is elastically deformed in the plastic deformation of the basebody. In the ideal state, it is attained that the internal tube restswith its full surface against the base body once the deformation isconcluded.

A further feature of the method of the invention is that during thedeformation of the base body, a mandrel is introduced into the internaltube. With the mandrel, an undesired plastic deformation of the internaltube during the deformation of the base body is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the invention will become apparent fromthe ensuing description, taken in conjunction with the drawings, inwhich:

FIG. 1 is a cross section of a first embodiment of a common rail of theinvention;

FIG. 2 is a fragmental longitudinal section of the common rail of FIG.1;

FIG. 3 is an enlarged view of the detail marked X in FIG. 2;

FIG. 4 is a fragmental longitudinal section of a second embodiment of acommon rail of the invention; and

FIG. 5 is a view of a section taken along the line V—V of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The common rail shown in FIGS. 1-3 is formed from a tubular base body 1.A connection bore 2 is disposed in the radial direction in the tubularbase body 1. The connection bore 2 has two segments 3 and 4 of differentinternal diameters. The segment 3 having the smaller diameter isdisposed on the side toward the interior of the tubular base body 1. Thesegment 4 of larger internal diameter follows the segment 3 having thesmaller internal diameter. A female thread 5 is embodied in the segment4 having the larger internal diameter. The female thread 5 in thesegment 4 of the connection bore 2 cooperates with a male thread that isembodied on the connection stub 6.

The segment 4 of the connection bore 2 having the larger internaldiameter serves to receive the end of a connection stub 6. A throughbore 7 is recessed out of the connection stub 6 and connects theinterior of the tubular base body 1 with a high-pressure fuel line (notshown). For securing the high-pressure fuel line, a female thread 8 isembodied in the head of the connection stub 6. On the outside, the headof the connection stub 6 is provided with a hexagonal contour 9. Thehexagonal contour 9 forms an engagement face for a tool.

By means of an elastic deformation of the connection stub 6, done fromoutside, the segment 3 of the connection bore 2 having the smallerdiameter is deformed elastically toward the interior of the tubular basebody 1. In FIG. 3, the contour of the critical region is indicated inthe unstressed state at 10 and in the stressed state at 11.

The end face of the connection stub 6 toward the interior of the tubularbase body 1 performs two functions in the present invention. First,pressing the end face of the connection stub 6 against the segment 3 ofthe connection bore 2 assures sealing off of the interior of the commonrail, subjected to high pressure, from its surroundings, and second, theend face of the connection stub 6 serves to transmit the requisite forcefor the deformation to the segment 3 of the connection bore 2.

The force required for the deformation is transmitted into the criticalregion of the segment 3 of the connection bore 2 having the smallerinternal diameter via the external hexagon 9, the male thread,complimentary to the female thread 5, of the connection stub 6, and theend face of the connection stub 6 toward the interior of the tubularbase body 1. By means of a defined attaching moment, the deformation canbe adjusted in a defined way.

Because material used is deformed elastically in the critical region atthe entrance to the bore, intrinsic pressure stresses can be introducedinto the region of the intersection without stress from pressure. Underthe internal pressure prevailing during operation, these intrinsicpressure stresses are then cancelled out. As a result, the region ofhigh tensile stresses is markedly reduced in size. In FIG. 3, it isindicated at 12 that in addition to the provisions of the invention, thecritical region is also rounded. The step 13 resulting from thedifferent internal diameters of the segments 3 and 4 of the connectionbore 2 is also called the bottom of the connection bore 2.

The second embodiment, shown in FIGS. 4 and 5, of a common rail of theinvention includes a tubular base body 21. A connection bore 22 extendsradially from the interior of the tubular base body 21. The connectionbore 22 discharges on the outside into a connection stub 23, which isembodied on the tubular base body 21. The connection stub 23 serves toconnect a high-pressure fuel line (not shown).

A circumferential groove 32 is embodied at the transition between theconnection stub 23 and the base body 21. The circumferential groove 32is engaged by a tool formed of two half-round tool halves 24 and 25. Thetwo tool halves 24 and 25 are subjected to force in the direction of thearrows 26 and 27 and are pressed against the tubular base body 21. As aresult, the tubular base body 21 deforms in the region of the connectionbore 22.

An internal tube 28 is disposed in the interior of the tubular base body21. A domelike indentation 29 is provided on the outer jacket face ofthe internal tube 28, in the region of the connection bore 22. A mandrelformed of two parts 30 and 31 is disposed in the interior of theinternal tube.

The internal tube 28 is positioned in the tubular base body 21 in such away that the domelike indentation 29 is located precisely in the regionof the connection bore 22. By pressing on the tubular base body 21 inthe region of the connection bore 22 with the tool 24, 25, the tubularbase body 21 is pressed into the domelike indentation 29 of the internaltube 28. In practical terms, the internal tube 28 forms the template forthe pressing operation. With the mandrel 30, 31, an undesired plasticdeformation of the internal tube 28 is prevented.

In the plastic deformation of the tubular base body 21, it is importantthat the internal tube 28 be elastically deformed jointly with it. Inthe ideal state, after the plastic deformation of the tubular base body21, the internal tube 28 rests with its full surface against the tubularbase body 21, at least in the region of the connection bore 22.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A method for producing a common rail for a commonrail fuel injection system of an internal combustion engine, the commonrail having a base body (1; 21) which is equipped with a plurality ofconnection openings (2; 22), the method comprising the step of deformingthe base body in the region of the connection openings (2; 22), whereinthe step of deforming the base body (1), in the region of the connectionopenings (2), comprises elastically deforming the base body from outsidewith the aid of a connection stub (6).
 2. The method of claim 1, furthercomprising providing a through bore in the region of each of theconnection opening, each said through bore having two segments (3, 4) ofdifferent-sized internal diameters.
 3. The method of claim 2, furthercomprising providing a female thread (5) in the segment (4) of thethrough bore (2) having the larger internal diameter.
 4. The method ofclaim 1, further comprising providing a through bore in the region ofeach connection opening, each through bore having two segments ofdifferent sized internal diameters, and providing each connection stub(6), on its end toward the common rail, with an outside diameter whichis substantially equal to the internal diameter of the segment (4) ofthe through bore (2) in the common rail having the larger diameter. 5.The method of claim 4, further comprising providing a male thread on theend of the connection stub (6) toward the common rail, the male threadbeing complimentary to the female thread (5) of the through bore (2). 6.A method for producing a common rail for a common rail fuel injectionsystem of an internal combustion engine, the common rail having a basebody (1; 21) which is equipped with a plurality of connection openings(2; 22), the method comprising the step of deforming the base body inthe region of the connection openings (2; 22), further comprisingproviding a rigid internal tube (28) in the base body, the internal tubehaving an outer contour which corresponds to the desired inner contourof the base body (21), in the region of the connection openings (22),and deforming the base body (21), in the region of the connectionopenings (22) from outside plastically inward with a tool (24, 25). 7.The method of claim 6, further comprising elastically deforming theinternal tube (28) in the plastic deformation of the base body (21). 8.The method of claim 6, wherein during the deformation of the base body(21), a mandrel (30, 31) is introduced into the internal tube (28). 9.The method of claim 7, wherein during the deformation of the base body(21), a mandrel (30, 31) is introduced into the internal tube (28). 10.The method of claim 1, further comprising providing a through bore inthe region of each of the connection opening, each said through borehaving two segments (3, 4) of different-sized internal diameters. 11.The method of claim 10, further comprising providing a female thread (5)in the segment (4) of the through bore (2) having the larger internaldiameter.
 12. The method of claim 4, further comprising providing afemale thread (5) in the segment (4) of the through bore (2) having thelarger internal diameter.
 13. The method of claim 12, further comprisingproviding a male thread on the end of the connection stub (6) toward thecommon rail, the male thread being complimentary to the female thread(5) of the through bore (2).
 14. The method of claim 7, wherein duringthe deformation of the base body (21), a mandrel (30, 31) is introducedinto the internal tube (28).
 15. A common rail for a common rail fluidinjection system of an internal combustion engine, comprising agenerally tubular base body, a plurality of connection openingsextending through the wall of said tubular base body, each saidconnecting opening including a through bore having a circular crosssection and each having segments of two different internal diameters, aconnection stub for each connection opening, each connection stub beingassembled to the tubular base body by being inserted into a connectionopening, and in the assembly process being brought to a final, assembledposition, each connection stub including means which elastically deformsthe material of the tubular base body as it is inserted into aconnection opening and brought to its final position on the tubular basebody.
 16. The common rail of claim 15, further comprising a femalethread formed in the segment of each through bore which has the largestdiameter.
 17. The common rail of claim 16, wherein each said connectingstub has an external diameter on an end adjacent said common rail whichis substantially equal to the internal diameter of the largest diametersegment of said through bore and having a male thread complimentary toand engaging said female thread of the through bore.
 18. A common railfor a common rail fluid injection system of an internal combustionengine formed by the method of claim
 1. 19. A common rail for a commonrail fluid injection system of an internal combustion engine formed bythe method of claim
 2. 20. A common rail for a common rail fluidinjection system of an internal combustion engine formed by the methodof claim 6.